Patent document 1 discloses a vehicular control apparatus, which includes a microcomputer (electronic control circuit) for in-vehicle communication and a power IC for supplying electric power to the microcomputer.
According to patent document 1, as shown by a flowchart in FIG. 11, when a sleep condition is satisfied (step S2: YES) by, for example, turn-off of an ignition switch of a vehicle, shutting off of a system (shutting off electric power supply to the microcomputer) from a normal control condition (step S1) is performed in the following manner.
In case that CAN, for example, is adopted as an in-vehicle LAN, the shutoff processing is executed (step S4) after completing preparation (CAN-Wakeup permission, step S3) so that the microcomputer may wake up when a dominant signal is transmitted to a communication bus and communication is started responsively. When the power IC shuts off a power voltage VOM supplied to the microcomputer, the power voltage VOM falls. When the microcomputer is reset (low-active) (step S5: YES), the microcomputer changes its state to a sleep state (step S6) and stops its operation.    (Patent document 1) JP 4032955 corresponding to US 2004/0122565
However, according the shutoff sequence in patent document 1, the microcomputer repeats an infinite loop of step S5 after outputting a shutoff command to the power IC. Thus the microcomputer waits for being reset. When any one of masters transmits a dominant signal to the communication bus for the in-vehicle communication as shown in FIG. 8 (refer to (c)) under this condition, the system starts the wake-up sequence. The power voltage VOM supplied by the power IC rises again (refer to (a)), but the microcomputer remains in the same condition (refer to (d)), in which the microcomputer repeats the infinite loop and waits for being reset. That is, the microcomputer remains deadlocked in the reset wait state, waiting for the reset signal being changed to low.
In case of an electronic control unit (ECU) for controlling a gear transmission of the vehicle, for example, a specification is provided such that a gear position in the transmission at that time is displayed on an instrument panel in the vehicle when a door of the vehicle opens or a driver seats on a driver's seat. According to this specification, the dominant signal is transmitted to a communication bus when the driver opens the door to get out of the vehicle after turning off an ignition switch. As a result, the deadlock state arises. To counter this problem, as shown in FIG. 13 for example, it is proposed to monitor whether a dominant signal (CAN Rx=H) is transmitted to the communication bus (step S7) during a period, in which the microcomputer waits for being reset at step S5 (NO).
However, a threshold value (for example, about 2V) provided so that a communication driver IC operable with CAN may detect the dominant signal differs from a high level threshold value (for example 3.5V) provided so that the microcomputer may recognize a Rx signal, which is an output signal of a communication driver IC. It is thus likely that the wakeup sequence is not performed normally because of difference in detection timing of the dominant signal and the Rx signal. In addition, each detection is performed in a period, in which the power voltage supplied to the microcomputer fluctuates, the difference in detection timing becomes greater. As a result, it is likely that the detection and recognition become different between the dominant signal and the Rx signal.